The present invention relates to a counterflow catalytic oxidizer with interactive dilution controls adapted for maintaining optimum operational efficiency during unattended continuous operation to purify an air stream and prevent pollution. Typically application of such catalytic oxidizers is for the destruction of vapors extracted insitu from contaminated soils requiring continuous operation for extended periods of time, typically measured in months. Such applications typically involve the clean-up of vapors in a potentially explosive environment where it is necessary to regulate the hydrocarbon content of the air stream by dilution to keep it below the lower explosive limit (LEL). The advantage of catalytic combustion is that it can be operated at a lower temperature and much lower hydrocarbon concentration than is possible with ordinary flame combustion.
The catalytic oxidizers used in hydrocarbon spill cleanup, such as the present invention, normally operate with inlet air hydrocarbon vapor mixture (inlet vapor) concentrations less than 25% of the lower explosive limit (LEL). The air hydrocarbon vapor mixture source may have much higher concentration, frequently in the explosive range. In such cases, the objective is to provide controlled dilution of the source stream with air, so as to maintain the inlet concentration of the inlet air hydrocarbon mixture to the catalytic unit within acceptable limits, but close to the maximum allowable, and provide for automatic relief and shutdown when the acceptable limits are exceeded as a safety measure.
Accordingly, it is desirable to provide an improved counterflow catalytic oxidizer with automatic dilution control that is portable, compact, that controls the concentration of inlet vapor for continuous unattended operation with safety shutdown and excess pressure protection. Also, it is desirable to provide a method of continuous oxidizing of hydrocarbon vapors employing the automatic dilution control system which is simple to operate, highly efficient, and explosion resistant.